The present invention is generally related to cellular telephone systems, and more particularly to an improved method for supervising time-division-multiple-access (TDMA) radio frequency (RF) communications in TDMA cellular telephone systems.
In TDMA cellular telephone systems, base station transmitters transmit different digital verification color codes (DVCCs) on active TDMA time slots of RF channels for enabling cellular telephones to determine if they are receiving their desired base station transmitter. The DVCCs are specified in TIA/EIA Interim Standard IS-54, paragraphs 2.4.3.1, 2.4.3.3 and 2.6.5.1, published by and available from the EIA Engineering Publications Office, 2001 Pennsylvania Ave., N.W., Washington, D.C. 20006. According to a prior technique complying with the IS-54 Standard, the DVCC being received on an active TDMA time slot during a telephone call is compared to the DVCC assigned during call setup or handoffs. If two consecutively received DVCCs match, then the telephone call may continue. If five consecutively received DVCCs do not match, then a five second timer is initiated. If two matching DVCCs have not been consecutively received during the five second time interval, then the cellular telephone call is terminated since the desired base station transmitter is no longer being received. However, such prior technique requires the use of a reasonably accurate internal timer, thereby necessitating additional hardware or software. Furthermore, the time base of this internal timer must match the time base of the base station in order to reliably meet the IS-54 Standard. For the foregoing reasons, there is a need for an improved method for supervising TDMA RF communications in TDMA cellular telephone systems, which does not rely on a timer and is simpler and more reliable than prior techniques.